The secondary usage of frequencies is being discussed as one countermeasure for relieving the depletion of frequency resources in the future. Secondary usage of frequencies refers to another system secondarily using some or all of the frequency channel preferentially allocated to a first system. Generally, the system to which the frequency channel is preferentially allocated is called the primary system, while the system that secondarily uses the frequency channel is called the secondary system. A typical example of a secondary system is a cognitive radio system.
TV white spaces are an example of frequency channels whose secondary usage is being discussed (see Non-Patent Literature 1). TV white spaces refer to channels, from among the frequency channels allocated to a television broadcasting system that acts as a primary system, which are not being used by that television broadcasting system depending on the geographical area. By opening up these TV white spaces to secondary systems, efficient frequency resource utilization may be realized. Non-Patent Literature 1 defines the technical requirements and operational requirements of a white space device (WSD) using a secondary system. A device that manages a secondary system is also called a master WSD, while a device that participates in a secondary system is also called a slave WSD.
During secondary usage of a frequency band, the secondary system ordinarily is demanded to be operated so as not to exert harmful interference on the primary system. One important technology for this purpose is transmit power control. For example, Patent Literature 1 and Patent Literature 2 disclose technology for restraining the aggregated interference that multiple secondary systems exert on the primary system to an allowed level.